The design and construction of arches is a technology that can be traced back to Roman times. Today arches are still used in a variety of structures including, culverts, bridges, tunnels and so forth.
Traditionally, arches constructed with component voussoirs are assembled by successively resting the voussoirs atop a shape support until a keystone, also known as the central voussoir, can be positioned. Once the keystone is positioned, the arch becomes self-supporting and the shape support can be removed. The shape support may be a frame, scaffolding, or simply a shaped pile of earth.
There are significant limitations to traditional methods of arch construction. The process can be complex and time consuming, requiring the pre-construction of the shape support or other means of support before the construction of the arch itself. Difficulties may be compounded if the area beneath the desired arch (for example, a roadway, a railway or a stream) is not to be obstructed during construction, or if only minimal environmental impact is acceptable.
In situations such as the construction of forestry roads for logging operations, it is desirable to be able to quickly and easily construct bridges over streams and other obstacles at remote locations with minimal damage or risk of damage to the waterways or obstacles in in question. To carry logging trucks and other heavy equipment, such bridges must be strong and reliable, Further, in many cases, such bridges must be easily removable at the end of a logging season or at the end of logging operations in a particular area. To facilitate both construction and removal, it generally can be said that such bridges should be made from components that are relatively few in number, easily transportable, and easy to assemble and disassemble using standard road building equipment such as commercially available excavators, front end loaders, light duty cranes and the like, and not equipment that needs to be custom built or specially adapted to handle the components, or to work with or around the components. Further, following assembly and disassembly at one site, the components preferably should be reusable at other sites,
Voussoir design is well known and numerous adaptations have been described in the prior art. For example, U.S. Pat. No. 884,498 (King) granted on Apr. 14, 1908, describes voussoirs each having an elongated flange extending along one load bearing end and an elongated shoulder recessed along an opposed load bearing end. The flange of each voussoir is sized to seat on the shoulder of an adjacent voussoir such that the outer surface of the flange also defines part of the extrados surface of the voussoir. However, in the absence of some form of securing means, the assembled arch appears to lack desirable stability. More particularly, it appears that with a correct application of external forces the voussoirs could slip longitudinally relative to one another along their abutting surfaces.
A similar observation may be made in reference to the block construction disclosed in U.S. Pat. No. 3,346,248 (Martinet et al) granted on Oct. 10, 1967. Individual blocks mate with an elongated tongue and groove arrangement rather than a shoulder and flange arrangement as disclosed by King. They are not used as arch voussoirs (they are intended as refractory blocks in a rotary kiln), but in principle similarly configured blocks could be used as voussoirs. But, the tongue and groove arrangement then would be prone to longitudinal slippage as in the case of King.
The problem of longitudinal slippage may be partially addressed in U.S. Pat. No. 758,417 (Clarke) granted on Apr. 26, 1904. In the case of Clarke, at least some of the voussoirs have a dog-leg configuration that is fittable with corresponding dog-legs in adjacent voussoirs. Thus, an external force that might produce longitudinal slippage between the voussoirs of King or Martinet et at may be resisted by the dog-leg fitting in the case of Clarke. However, a force in the opposite direction (viz, one tending to separate the dog-leg fitting) could still produce slippage. Further, the use of dog-legged voussoirs or other irregularly shaped voussoirs having more than 6 major surfaces (viz. intrados, extrados, two opposed sides, and two opposed end bearing surfaces) may be considered undesirable for at least two reasons. Firstly, the structure of individual voussoirs is more complex and may be inherently less rugged and weaker than a simple 6-sided structure. Secondly, an excess number of specially configured additional voussoirs may be required in order to properly finish a completed arched structure. In this regard, the dog-legged structure disclosed by Clarke would require a number of L-shaped voussoirs and a number of rhomboid-shaped voussoirs in addition to the dog-legged voussoirs. Otherwise, a series of unsupported gaps would appear along opposed sides of a completed arched structure.
In each case, King, Martinet et al. and Clarke would all appear to require the use of a shape support during the construction phase of an arched structure made with their blocks or voussoirs.
U.S. Pat. No. 663,204 (White) granted on Dec. 4, 1900, describes a fireproof construct on having an arch configuration wherein pairs of arch blocks or voussoirs forming opposed sides of the arch each have a lower end adapted to rest on the foot of an I beam, and an upper end tied back to the top of the I-beam to provide a form of internal stability. However, it is not clear how the 1-beams themselves are stabilized either during construction or thereafter. Further, the blocks themselves are questionably characterized as voussoirs. Each block sweeps an angle of 90° and the overall structure does not include a central voussoir or keystone. Thus, the size of the blocks is large (each has a span that necessarily transcends one-half the horizontal span of the arch), and arch assembly and disassembly likely would require heavy duty or special purpose equipment not normally used in road construction.
It is an object of the present invention to provide a new and improved arched structure that is easy to assemble and disassemble without the need for an underlying support structure, and that may be constructed using voussoirs that are easily fabricated, rugged, and that are easily transportable in their disassembled condition.
A further object of the present invention is to provide a voussoir with features enabling an improved interlock with like voussoirs, the interlock serving not only to resist slippage between adjacent voussoirs but also to enhance the ease of assembling an arched structure.
Yet another object of the present invention is to provide a new and improved method of constructing an arched structure without the need for the use of an underlying support structure during construction.